Nowadays, mobile electronic devices such as mobile phones, personal digital assistants (PDAs), laptop computers, MP3 players, and so on, are in widespread use around the world. Mobile electronic devices are getting smaller and lighter for even more portability and convenience, while at the same time becoming increasingly capable of performing more advanced functions and services, both due to the development of the devices and the network systems.
While for convenience sake, it is often desirable that these devices be small and lightweight, they still need to possess a certain structural strength so that they will not be damaged in normal handling and occasional drops. Thus, usually built into such devices are structural parts whose primary function is to provide strength and/or rigidity and/or impact resistance to the device, and possibly also provide mounting places for various internal components of the device and/or part or all of the mobile electronic device case (outer housing), while ensuring electrical insulation/electrical shield among components. While in the past, low density metals such as magnesium or aluminium, were the materials of choice, synthetic resins have progressively come as at least partial replacement, for costs reasons (some of these less dense metals such as magnesium are somewhat expensive, and manufacturing the often small and/or intricate parts needed is expensive), for overriding design flexibility limitations, for further weight reduction, and for providing un-restricted aesthetic possibilities, thanks to the colorability of the same. Plastic parts of such devices are hence made from materials that are easy to process into various and complex shapes, are able to withstand the rigors of frequent use, including outstanding impact resistance, generally possess electrical insulating capabilities, and which can meet challenging aesthetic demands while not interfering with their intended operability.
Nevertheless, in certain cases, plastics may not have the strength and/or stiffness to provide for all-plastic structural parts in mobile electronic devices, and metal/synthetic resins assemblies are often encountered.
In these cases, metal parts, e.g. aluminum parts and/or aluminium/plastic composite parts present in mobile devices, are submitted generally to anodization, i.e. to electro chemical processes where the aim is to build an oxide layer on the aluminum surface, notably through the use of aggressive chemicals. In this regards, anodization being performed on parts already comprising/assembled to polymeric elements, polymeric materials used are required to exhibit excellent chemical resistance to various aggressive acids.
As said, it is desirable that such plastic materials for mobile devices have good impact resistance, tensile strength, stiffness and that they exhibit minimal warpage when they are formed (as by injection molding, for example) into the intended complex shape, designed to be assembled with minimum tolerance with a large number of additional structural and functional components.
The warpage is a term designating dimensional distortion in the molded parts leading to their concave or convex curvature. An inherent shrinkage occurs during any injection molding process because the density of the polymer varies from the processing temperature to the ambient temperature. During injection molding, the variation in shrinkage creates internal stresses which lead to the warpage of the part upon ejection from the mold. If the shrinkage throughout the part is uniform, the molded part will not deform or warp, it will simply become smaller. However, providing polymer materials delivering uniform shrinkage remains a challenge.
An additional requirement for plastics material used in mobile electronics part is that they shall be resistant to staining agents that are often put in contact with these portable electronic devices housings. Typical staining agents include: makeup (such as lipstick, lip gloss, lip liner, lip plumper, lip balm, foundation, powder, blush), artificial or natural colorants (such as those found in soft drinks, coffee, red wine, mustard, ketchup and tomato sauce), dyes and pigments (such as those found in dyed textiles and leather, used for the manufacture of portable electronic devices housings). In contact with these staining agents, the portable electronic devices housings maybe easily stained: anti-stain properties are hence much appreciated for maintaining aesthetic appearance of said portable devices, in particular when the same are bright coloured or in shades of white or clear colours.
Providing a polymeric composition fulfilling all afore-mentioned requirements, that is to say possessing adequate mechanical performances for ensuring structural support (tensile strength) and yet a certain flexibility for enabling mounting/assembling (elongation at break), able to withstand to impact and to aggressive chemicals, having colorability and stain and UV-resistance is a continuous challenge in this field, and while solutions based on a variety of plastics have already been attempted, still continuous improvements to reach unmet challenges are required.